This invention relates to photographic apparatus for use with transmission electron microscopes (TEM). More particularly, it concerns such apparatus which is adaptable to presently existing TEM machinery designs without modification of that machinery and which makes possible TEM exposure and immediate processing of instant film exemplified by diffusion transfer film emulsions and related processing chemistry.
TEM machines are capable of providing an image of a specimen with a magnification factor of up to one million times and are used extensively in such fields as pathology, biology, chemistry, metallurgy and other industrial applications for visible observation of such magnified images. Although the magnified electron image may be observed directly when focused on a fluorescent screen or by using other forms of electronic imaging devices, the resolution of detail in such directly observable images is much lower than the resolving capacity of photographic emulsions. For this reason, as well as for providing permanent records of TEM magnified images of specimens, TEM machines are conventionally equipped with photographic film exposing systems to enable visual observation of high resolution detail in the magnified specimen image. Moreover, final analyses of a given specimen is usually delayed until one or more photographs of the TEM image are available for observation.
TEM machines are extremely expensive, currently priced in the hundreds of thousands of U.S. dollars, and as such, each machine represents a major investment to a research laboratory. In addition to costly, high power electron beam generating and focusing components, the space or chamber in which the electrons are transmitted must be evacuated to 10.sup.-7 atmospheric pressure or more in order to avoid electron scattering by collision with molecules of air or with molecules of other substances in a gaseous phase. In this latter respect, it is to be noted that all normally liquid and any normally solid substances will vaporize under the magnitude of vacuums developed in the electron chamber of TEM machines. Because the film and film handling accessories of a TEM photographic system are presented in the evacuated electron beam chamber and, moreover, are passed into and out of that chamber, each TEM machine involves costly vacuum sealing mechanisms predicated in substantial part on the physical format of film unit assemblies employed and on the configuration of film containers or boxes to be used in a TEM machine of a given design. Hence, modification of photographic components in presently existing TEM equipment is impractical and, moreover, design changes in photographic apparatus supplied by manufacturers of TEM machines are restricted to accommodation of respective TEM machine designs.
To provide a general understanding of existing TEM machine design and the procedures required in the handling of photographic film to be used in such machines, reference is made to FIGS. 1 and 2 of the accompanying drawings. In FIG. 1, the various photographic equipment and handling procedures in a conventional research laboratory are schematically represented. In FIG. 2, the transfer of individual film units within the TEM machine is diagrammatically depicted.
In FIG. 1, a TEM machine 10 is shown to include a cabinet-like base 12 on which is mounted an electron beam focusing column 14 having a specimen receptor 16 and carrying an electron beam generating head 18 at its upper end. An observation port 20 is customarily provided for viewing a fluorescent plate (not shown) at the base of the column. The cabinet 12 includes a pair of drawers 22 and 24 for receiving respectively a film supply box 26 and a film receiver box 28. In FIG. 2, the film boxes 22 and 24 are shown as they might be oriented within the TEM machine 10 which includes mechanisms (not shown) for transferring individual film units 30 from the supply box 26 to an exposure station aligned with the focusing column 14 and then to the receiver box 28. The evacuated chamber of the TEM machine 10 is generally depicted in phantom lines in FIG. 2 and as such encloses both boxes 26 and 28 within the machine 10.
The film handling procedure now used in TEM laboratories is diagrammatically depicted in FIG. 1 of the drawings. Individual film sheets 32 are removed from a shipping carton 34, manually inserted into a machine compatible carrier plate 36 to provide a film unit 30. The film units 30 are then loaded into a supply box 26 to complete a film preparation procedure carried out in total darkness within a darkroom 38. In larger TEM laboratories, as many as 8 or more TEM machines 10 may be serviced by a single darkroom. Also, it is not uncommon for a laboratory to employ the TEM machines of two or more different manufacturers, each of which requires a unique carrier plate 36, supply box 26 and receiver box 28. Both boxes 26 and 28 employ lighttight cover or "dark slide", the dark slide 40 of the supply box 26 being closed in the darkroom 38 after it is filled with film units 30.
Prior to use in a TEM machine 10, the loaded supply boxes 26 must be out-gassed in a vacuum chamber 42 for at least 12 hours to assure removal of volatile substances which may vaporize in the vacuum chamber of the TEM machine. As explained above with reference to FIG. 2, in the TEM machine 10, a specimen is inserted into the column 14 and photographed by passing the individual film units 30 from the supply box 26 to an exposure station and then to the receiver box 28. It is desirable with some types of specimens to expose only a few film units 30 and then remove the receiver box 28 (with only the few exposed film units) and return it to the darkroom for development so that the developed images may be observed prior to making further exposures of electron images of the same specimen. In fields such as pathology or where other biological specimens are under observation, the time required for conventional film handling development is often longer than the viable life of the specimen. Hence, it is customary to await development of film until the receiver box 28 is filled.
From the foregoing, it will be appreciated that in the present use of TEM machinery, the attainment of a high resolution photograph of a specimen is a very tedious and time consuming procedure by which the benefits of specimen analysis are significantly delayed. This is particularly true in the field of pathological analysis of tissue removed by surgery or in similar fields where it would be desirable to have the benefit of a TEM photograph available within a short period of time.